On Thu, Oct 29, 2015 at 12:49 PM, David Malcolm <dmalc...@redhat.com> wrote:
> Attempting to bootstrap gcc with -Wmisleading-indentation enabled I ran
> into a few failures where the indentation, although bad, was arguably
> not misleading.
>
> In regrename.c:scan_rtx_address:
>
> 1308 case PRE_MODIFY:
> 1309 /* If the target doesn't claim to handle autoinc, this must be
> 1310 something special, like a stack push. Kill this chain. */
> 1311 if (!AUTO_INC_DEC)
> 1312 action = mark_all_read;
> 1313
> 1314 break;
> ^ this is indented at the same level as the "action =" code,
> but clearly isn't guarded by the if () at line 1311.
>
> In gcc/fortran/io.c:gfc_match_open:
>
> 1997 {
> 1998 static const char *delim[] = { "APOSTROPHE", "QUOTE",
> "NONE", NULL };
> 1999
> 2000 if (!is_char_type ("DELIM", open->delim))
> 2001 goto cleanup;
> 2002
> 2003 if (!compare_to_allowed_values ("DELIM", delim, NULL, NULL,
> 2004
> open->delim->value.character.string,
> 2005 "OPEN", warn))
> ^ this is indented with the "goto cleanup;" due to
> lines 2000-2001 not being indented enough, but
> line 2003 clearly isn't guarded by the
> "if (!is_char_type" conditional.
>
> In gcc/function.c:locate_and_pad_parm:
>
> 4118 locate->slot_offset.constant = -initial_offset_ptr->constant;
> 4119 if (initial_offset_ptr->var)
> 4120 locate->slot_offset.var = size_binop (MINUS_EXPR, ssize_int
> (0),
> 4121
> initial_offset_ptr->var);
> 4122
> 4123 {
> 4124 tree s2 = sizetree;
> 4125 if (where_pad != none
> 4126 && (!tree_fits_uhwi_p (sizetree)
> 4127 || (tree_to_uhwi (sizetree) * BITS_PER_UNIT) %
> round_boundary))
> 4128 s2 = round_up (s2, round_boundary / BITS_PER_UNIT);
> 4129 SUB_PARM_SIZE (locate->slot_offset, s2);
> 4130 }
> ^ this block is not guarded by the
> "if (initial_offset_ptr->var)"
> and the whitespace line (4122) is likely to make a
> human reader of the code read it that way also.
>
> In each case, a blank line separated the guarded code from followup code
> that wasn't guarded, and to my eyes, the blank line makes the meaning of
> the badly-indented code sufficiently clear that it seems unjustified to
> issue a -Wmisleading-indentation warning.
This makes sense to me.
Though I've been thinking about proposing a simpler and more relaxed heuristic:
if (next_stmt_exploc.line - body_exploc.line > 1)
return false;
That is, don't warn if there are any lines between the (start of the)
body statement and the next statement.
This would catch the presence of blank lines as well as code like:
if (foo)
bar (an_argument_1,
an_argument_2);
baz ();
and
if (foo)
bar ();
/* Some comment. */
baz ();
Though I am not confident that we should not warn in such cases. At
this point whether some code is misleadingly indented or not becomes
pretty subjective (so it may be better to not warn?)
>
> The attached patch suppresses the warning for such a case.
>
> OK for trunk?
>
> gcc/c-family/ChangeLog:
> * c-indentation.c (line_is_blank_p): New function.
> (separated_by_blank_lines_p): New function.
> (should_warn_for_misleading_indentation): Don't warn if the
> guarded and unguarded code are separated by one or more entirely
> blank lines.
>
> gcc/testsuite/ChangeLog:
> * c-c++-common/Wmisleading-indentation.c (fn_40): New function.
> ---
> gcc/c-family/c-indentation.c | 58
> ++++++++++++++++++++++
> .../c-c++-common/Wmisleading-indentation.c | 32 ++++++++++++
> 2 files changed, 90 insertions(+)
>
> diff --git a/gcc/c-family/c-indentation.c b/gcc/c-family/c-indentation.c
> index 5b119f7..d9d4380 100644
> --- a/gcc/c-family/c-indentation.c
> +++ b/gcc/c-family/c-indentation.c
> @@ -77,6 +77,42 @@ get_visual_column (expanded_location exploc,
> return true;
> }
>
> +/* Determine if the given source line of length LINE_LEN is entirely blank,
> + or contains one or more non-whitespace characters. */
> +
> +static bool
> +line_is_blank_p (const char *line, int line_len)
> +{
> + for (int i = 0; i < line_len; i++)
> + if (!ISSPACE (line[i]))
> + return false;
> +
> + return true;
> +}
> +
> +/* Helper function for should_warn_for_misleading_indentation.
> + Determines if there are one or more blank lines between the
> + given source lines. */
> +
> +static bool
> +separated_by_blank_lines_p (const char *file,
> + int start_line, int end_line)
> +{
> + gcc_assert (start_line < end_line);
> + for (int line_num = start_line; line_num < end_line; line_num++)
Shouldn't this loop begin at start_line + 1?
